Rotary gate valves are well known. For example, British patent number GB2340917 describes a rotary gate valve comprising a housing that supports or defines a valve seat and contains a valve gate member. The valve seat has an inlet port and an outlet port, and fluid communication therebetween is controlled by the valve gate member. The valve gate member is angularly moveable between a closed position in which it seals at least one of the inlet and outlet ports, and an open position in which fluid can flow between the inlet and outlet ports, via the valve gate member. A contacting face of the valve gate member is maintained in sliding contact with the valve seat throughout the range of movement (from closed to open positions), and the contacting face of the valve gate member forms a metal to metal seal with the valve seat in the closed position. In some arrangements, the valve gate includes at least one gate button, each of which comprises a circular contacting face. Each gate button has a circular cross section, and the circular contacting face is larger in diameter than the circular port of the valve seat that is sealed thereby in the closed position. The gate buttons are spring biased into engagement with, and so exert a load on, the valve seat. In the fully closed position, the circular contacting face of the gate button is concentric with the circular port that it seals.
In such an arrangement, the valve gate member includes a pair of flow passages which substantially align, when the valve gate member occupies its fully open position, with the inlet and outlet ports. The flow passages open into a chamber located to the opposite side of the valve gate member from the valve seat. It will be appreciated, therefore, that when the valve gate member occupies an open position, fluid is able to flow from the inlet port to the above mentioned chamber via the flow passage that is substantially aligned with the inlet port, and from the above mentioned chamber through the other of the flow passages to the outlet port.
Depending upon the application in which the valve is used, fluid may further be permitted to flow in the reverse direction.
It will be appreciated that in flowing between the inlet and outlet ports in the manner described above, the fluid must undertake several very sharp changes in direction, for example as it flows between the passages and the chamber. Furthermore, the movement of the gate valve member between its open and closed positions is typically transmitted thereto via a shaft or spindle extending through the above mentioned chamber, and so further fluid flow direction changes must be undertaken in order for the fluid to pass around the shaft or spindle.
The fluid flow direction changes may result in increased turbulent fluid flow within the gate valve. Potentially, parts of the valve may be damaged by erosion or increased wear. Furthermore, and importantly, the sharp changes in flow direction can result in the formation of a restriction to fluid flow and so reduce the rate at which fluid can flow through the valve.